Strip rolling mill and strip rolling method

ABSTRACT

To preferably roll a hard material or an ultra thin material by more reliably supporting small diameter work rolls even under a transient condition such as when starting a rolling operation or when finishing a rolling operation, undriven both ends support rolls  9, 10, 11  and  12  are provided on outer sides of a width along which a maximum sheet width of strip passes on a barrel portion of the work roll  3 , to be opposed to each other at an entry side and a delivery side of respective end portions to thereby press and support the work roll. Further, hydrostatic bearings  21  and  23  are installed at central portions of both side barrels of the work roll  3 , and fluid such as oil is supplied from fluid pressure supply ports  25  and  26  to the bearing portions to thereby float up the work rolls  3  by forming gaps between the hydrostatic bearings  21  and  23  and the work roll  3  and support the work roll  3  in horizontal direction in noncontact. By changing supply pressure of the fluid supplied to the hydrostatic bearings  21  and  23 , a proper float up amount and a support force can be set or controlled.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a strip rolling mill, and more particularly to a strip rolling mill and a strip rolling method suitable for high quality milling for a hard material and an ultra thin material using a small diameter work roll.

[0002] Conventionally, a work roll having a small diameter has been used when rolling a hard material such as stainless steel or an ultra thin material. When the diameter of a work roll is reduced, naturally, the bending rigidity of the roll is reduced and particularly, bending in a horizontal plane produces a problem. The horizontal bending causes a deterioration in shape (flatness) of strip.

[0003] In consideration of the above, there has been developed a multiple stage rolling mill of a cluster type such as a Sendzimir mill and a rolling mill having a horizontal bending preventive mechanism that supports a barrel portion of a work roll by a support roll from the horizontal direction as disclosed in Japanese Patent Laid-Open No. Sho 60-18206. However, in these rolling mills, the work roll is supported by using the support roll divided in a barrel length direction of the work roll. Therefore, there is a problem that the surface condition of strip is deteriorated by a trasnfer mark caused by the divided support rolls.

[0004] In order to deal the above-mentioned deterioration of strip, Japanese Patent Laid-Open No. Hei 1-262005 discloses a method in which divided rolls are not used, slide bearing pads which are brought into sliding contact directly with an entry side and a delivery side of a work roll in the horizontal direction are disposed, and a displacement in the horizontal direction is controlled by pressing the slide bearing pads to thereby carry out control in shape of strip.

[0005] According to the method, since the work roll is supported by sliding the bearing pad relative to the work roll and accordingly, when the lubricating condition is poor, there are caused damage and seizure phenomenon by direct sliding motion on the surface of the work roll and the damage is transferred onto the surface of the strip, resulting in deterioration of the strip quality.

[0006] As a method of resolving such a problem, Japanese Patent Laid-Open No. Hei 2-147108 and Japanese Patent Laid-Open No. Hei 10-230308 disclose a rolling mill having a horizontal direction support mechanism for supporting a work roll by hydrostatic bearings while interposing idle rolls therebetween without slidably supporting the work roll directly by slide bearing pads.

[0007] Further, there is a problem that under uncontinuous conditions such as when starting a rolling operation (in biting strip), a force to make a work roll significantly bend is generated and exerted to a hydrostatic bearing, a gap between the hydrostatic bearing and an idle roll is reduced and finally, the hydrostatic bearing and the idle roll are brought into contact with each other. In order to prevent the problem, Japanese Patent Laid-Open No. Hei-11347607 discloses a technology of “providing stopper means for preventing a gap between a hydrostatic bearing and a work roll or an idle roll supported by the hydrostatic bearing from becoming less than a predetermined value”.

[0008] According to Japanese Patent Laid-Open No. Hei 11-347607, specifically, the stopper means is constituted by gap defining rolls which are brought into contact with the work roll at positions in the axial direction on outer sides of an area in correspondence with a maximum sheet width of strip substantially from the horizontal direction and functions to prevent the gap between the hydrostatic bearing and the idle roll from becoming less than the predetermined value.

[0009] In the meantime, Japanese Patent Laid-Open No. Hei 9-285804 disclose a technology in which a work roll is pressed and horizontally supported by both ends support rolls only at outer sides of a strip pass (outer sides of a maximum sheet width of strip) of the work roll whose contact positions is the same as those of the above-described gap defining rolls.

[0010] However, according to the technology of Japanese Patent Laid-Open No. Hei 11-347607, the gap defining rolls at the both end portions basically serve as stoppers for preventing horizontal movement of the work roll and accordingly, when rolling operation is not carried out, the gap defining rolls do not apply a press force to the both end portions of the work roll and a very small interval is present therebetween or the gap defining rolls are brought into slight contact with the both end portions of the work roll.

[0011] Therefore, under a transient condition such as when starting a rolling operation (in biting strip), there are various problems that when load is applied suddenly from a state in which the gap defining rolls are not rotated, the work roll and the gap defining rolls are slipped relative to each other, damage is caused and transferred onto the respective rolls, and abrupt shock load is caused at an instance at which the gap defining rolls are brought into contact with the work roll and the bearing portion is destructed.

[0012] Further, a horizontal load generated at the work roll when rolling is not shared and is not supported by the gap defining rolls and accordingly, all of rolling load is shared by the hydrostatic bearings. Thus, there is a problem that not only when starting a rolling operation (in biting strip) but also when finishing a rolling operation (in tailing out strip), the static bearings receive abrupt shock load and thereby the idle rolls are liable to be brought into contact with the static bearings.

[0013] In contrast thereto, according to the technology of Japanese Patent Laid-Open No. Hei 9-285804, since hydrostatic bearings are not provided, all of horizontal load generated at the work roll is supported only by the both ends support rolls installed at comparatively narrow areas on outer sides of the strip pass of the work roll, resulting in a problem of service life of bearings of the both ends support rolls.

[0014] It is an object of the present invention to provide a strip rolling mill and a strip rolling method suitable for more reliably supporting a small diameter work roll to provide a high quality hard material or an ultra thin material without transferring damage caused by slip between rollers and without causing damages of bearing portions of respective rolls that will be caused by abrupt shock load even under a transient condition such as when starting a rolling operation or when finishing a rolling operation.

SUMMARY OF THE INVENTION

[0015] (1) In order to achieve the above-described object, according to an aspect of the present invention, there is provided a strip rolling mill comprising: at least a pair of upper and lower work rolls for rolling strip; at least a pair of backup rolls for supporting the work rolls in an up and down direction and providing a rolling drive force thereto; at least pairs of both ends support rolls opposed to each other in a horizontal direction for pressing and sandwiching both end portions of the work rolls on outer sides of a width along which a maximum sheet width of the strip passes on barrel portions of the work rolls; and hydrostatic bearings for supporting, by hydraulic pressure, at least either one of an entry side and a delivery side of centers of the barrel portions of the work rolls substantially in a horizontal direction.

[0016] Thus, bending of the work roll in the horizontal direction caused under a rolling transient condition as when starting a rolling operation or when finishing a rolling operation can effectively be shared by means of the both ends support rolls and the hydrostatic bearings to thereby surely support the work roll.

[0017] (2) Further, in order to achieve the above-described object, according to another aspect of the present invention, there is provided a strip rolling mill comprising: at least a pair of upper and lower work rolls for rolling strip; at least a pair of backup rolls for supporting the work rolls in an up and down direction and providing a rolling drive force thereto; at least pairs of both ends support rolls opposed to each other in a horizontal direction for pressing and sandwiching both end portions of the work rolls on outer sides of a width along which a maximum sheet width of the strip passes on barrel portions of the work rolls; and hydrostatic bearings for supporting, by hydraulic pressure via at least one or more of idle rolls, at least either one of an entry side and a delivery side of centers of the barrel portions of the work rolls substantially in a horizontal direction.

[0018] Thus, the bending of the work roll in the horizontal direction can effectively be shared by means of the both ends support rolls and the hydrostatic bearings to thereby surely support the backup roll, and even if the work roll is ground and the diameter is changed, the work roll can pertinently be supported always by the hydrostatic bearings via contact with the idle rolls.

[0019] (3) In the strip rolling mill of (1) or (2), preferably, a total support apparatus integrally formed by support portions for the both ends support rolls and support portions for the hydrostatic bearings are installed to be capable of adjusting the position of the work rolls in the horizontal direction at either one of the entry side and the delivery side of the work rolls as a reference side; and wherein on opposed sides of the work rolls, as pressing side, the total support apparatus are installed to be capable of pressing the work rolls in the horizontal direction opposedly to the reference side.

[0020] Thus, by only setting positional relationship of the respective both ends support rolls with respect to the respective total support apparatus, the relative positional relationship with respect to the hydrostatic bearings can simply and accurately be set and the work rolls can be supported pertinently.

[0021] (4) In the strip rolling mill of (1) or (2), preferably, when supporting the work roll by the hydrostatic bearing, the work roll is supported on a side of receiving a load by rolling and on an opposed side, the work roll is supported in noncontact or slight contact with the hydrostatic bearing.

[0022] Thus, the work roll is preferably supported without applying extra load to the hydrostatic bearing on the side that receives the roll by rolling.

[0023] (5) In the strip rolling mill of any one of (1) through (4), preferably, the strip rolling mill further comprises load detecting means provided at support portions for at least one of the both ends support rolls on at least one of the entry side and the delivery side and for at least one of the hydrostatic bearings.

[0024] Thus, the position of the hydrostatic bearing in the horizontal direction can be set and controlled such that the hydrostatic bearing can support the work roll by a pertinent support force.

[0025] (6) In the strip rolling mill of any one of (1) through (5), preferably, the support force in the horizontal direction of the both ends support roll supporting portions on the reference side is controlled to be larger than a slip occurrence limit value between the work rolls and the both ends support rolls but to be smaller than a support limit value of the both ends support rolls; and wherein the press force of the both ends support rolls on the pressing side is controlled to be larger than the slip occurrence limit value between the work rolls and the both ends support rolls and to be as large as possible within a range equal to or smaller than the support limit value of the both ends support rolls.

[0026] Thus, occurrence and transfer of damage caused by slip between the rolls are prevented, damage of the bearing portions of the respective rolls caused by high load is prevented, and the work roll can be supported more reliably.

[0027] (7) In the strip rolling mill of any one of (1) through (6), preferably, the strip rolling mill further comprises means for variably controlling an effective length of the hydrostatic bearing to be substantially the same as a sheet width of the strip.

[0028] Thus, press and support forces to be exerted to the work roll become minimum in necessity and accordingly, the bending of the work roll is minimized and stability in supporting the both ends of the work roll is promoted since directions of reaction at the both end support portions are not reversed but become constant.

[0029] (8) According to an aspect of the present invention, there is provided a strip rolling method of rolling strip by supporting the work rolls in the horizontal direction by means of the both ends support rolls and the hydrostatic bearings using the strip rolling mill according to (1) or (2).

[0030] With the method, the bending of the work roll in the horizontal direction caused under the rolling transient condition such as when starting a rolling operation or when finishing a rolling operation is shared effectively by means of the both ends support rolls and the hydrostatic bearings to thereby surely support the work roll.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a vertical sectional view of principal portions of a strip rolling mill according to a first embodiment of the present invention;

[0032]FIG. 2 is a horizontal sectional view of principal portions of the strip rolling mill according to the first embodiment of the present invention;

[0033]FIG. 3 is a view for explaining the force S in the horizontal direction exerted to a small diameter work roll;

[0034]FIG. 4A is a model diagram of support for horizontal bending caused in a work roll by rolling and FIG. 4B illustrates a bending amount δ caused in the work roll;

[0035]FIG. 5 is a diagram showing a change of axial bending δ when rolling conditions such as a sheet width W and a work roll support system are changed;

[0036]FIG. 6 is a diagram representing a calculating result of reaction Rc of both ends supporting points, when rolling conditions such as the sheet width W and the work roll support system are changed, in a ratio thereof to a value (a₀) in the case of both ends simple support;

[0037]FIG. 7 is a view showing a constitution in which two or more of both ends support rolls are installed on one side of respective end portions of a work roll;

[0038]FIG. 8 is a view showing a constitution that changes an effective support length of a hydrostatic bearing in accordance with a sheet width;

[0039]FIG. 9 is an explanatory view of the force S in the horizontal direction exerted to a work roll when there is a positional shift (offset) in a rolling pass direction between the work rolls and intermediate rolls supporting the work roll from an up and down direction;

[0040]FIG. 10 is a vertical sectional view of principal portions of a strip rolling mill according to a second embodiment of the present invention;

[0041]FIG. 11 is a horizontal sectional view of principal portions of the strip rolling mill according to the second embodiment of the present invention;

[0042]FIG. 12 is a vertical sectional view of principal portions of a strip rolling mill according to a third embodiment of the present invention; and

[0043]FIG. 13 is a horizontal sectional view of principal portions of the strip rolling mill according to the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] Embodiments of the present invention will be described in reference to the drawings.

[0045]FIG. 1 is a vertical sectional view of principal portions of a strip rolling mill 1 according to a first embodiment of the present invention and FIG. 2 is a horizontal sectional view of principal portions of the strip rolling mill 1.

[0046] In these drawings, a pair of work rolls 3 and 4 to roll strip 2 are supported in the vertical direction by intermediate rolls 5 and 6 and backup rolls 7 and 8. The intermediate rolls 5 and 6 are connected to a motor, not illustrated, and the work rolls 3 and 4 are driven by the intermediate rolls 5 and 6.

[0047] Undriven both ends support rolls 9, 10, 11 and 12 are installed on an entry side and a delivery side of respective end portions to be opposed to each other on outer sides of a width along which a maximum sheet width of the strip passes on barrel portions of the work roll 3.

[0048] In this embodiment, a rolling pass direction of the strip 2 is a direction directed from left to right. A left side of the work roll 3 is defined as a rolling pass direction position setting side (hereinafter, referred to as reference side) of the work roll 3 and a right side opposed thereto is defined as a pressing side.

[0049] Further, the both ends support rolls 10 and 12 on the reference side are attached to both ends support roll position setting apparatuses 13 and 14 disposed in the horizontal direction with respect to the work rolls, and the both ends support roll position setting apparatuses 13 and 14 are fixed to housing posts 16 and 18.

[0050] Although according to this embodiment, a motor-driven screw type is shown for the both ends support roll position setting apparatus 13 and 14, other constitution such as a fixed type or a hydraulic cylinder having a position adjusting function may be adopted.

[0051] Further, the both ends support roll position setting apparatus 13 and 14 are provided with both end support force detecting apparatuses 19 and 20 which are load detecting means for detecting load from the work roll 3 so that a sum of load generated at both end portions of the work roll 3 and a press force from the both ends support rolls 9 and 11 opposed to each other can be detected.

[0052] Further, hydrostatic bearings 23 and 24 at barrel center portions of the work rolls 3 and 4 on the reference side are disposed so that a fluid such as oil is supplied from a fluid pressure supply port 25 to the bearing portions, a gap is produced between the hydrostatic bearing 23, and the work roll 3 to thereby float up the work roll 3 and the work roll 3 is supported in the horizontal direction in noncontact. There is employed a constitution in which by changing supply pressure of the fluid supplied to the hydrostatic bearings 23 and 24, a proper float up amount and a support force can be set or controlled.

[0053] The hydrostatic bearings 23 and 24 are respectively installed at beams 29 and 30 having high rigidity and the rigid beams 29 and 30 are installed further to hydrostatic bearing position setting apparatuses 33 and 34 fixed to the housings 16 and 18.

[0054] The hydrostatic bearing position setting apparatuses 33 and 34 set and control the gap between the hydrostatic bearing 23 and the work roll 3 to suitably support a work roll horizontal force generated when rolling operation. Further, the hydrostatic bearing position setting apparatuses 33 and 34 are provided with hydrostatic support force detecting apparatus 35 and 36 such that a support force of the hydrostatic bearing 23 can be detected.

[0055] In the meantime, on the pressing side (right side of FIG. 2) opposed to the rolling pass direction position setting side (reference side) of the work roll 3, the both ends support rolls 9 and 11 on the pressing side capable of being pressed by both ends support roll pressing apparatuses 37 and 38 fixed to housings 15 and 17 are installed at positions opposed to positions of the both ends support rolls 10 and 12 on the reference side.

[0056] Further, the both ends support roll pressing apparatus 37 and 38 are provided with both end pressing force detecting apparatuses 39 and 40 which are load detecting means such that a press force of the both ends support rolls on the pressing side can be detected.

[0057] Although the both ends support roll pressing apparatuses 37 and 38 are cylinders in FIG. 2, a fixed type or a screw type may be adopted. In that case, it is necessary to use load cells or the like as the both end pressing force detecting apparatuses 39 and 40.

[0058] Further, hydrostatic bearings 21 and 22 are installed at barrel center portions of the work rolls 3 and 4 on the pressing side so that a fluid such as oil is supplied from a fluid pressure supply port 26 to the bearing portions, a gap is produced between the hydrostatic bearing 21 and the work roll 3 to thereby float up the work roll 3, and the work roll 3 is pressed and supported in the horizontal direction in noncontact.

[0059] Beams 27 and 28 having large rigidity are disposed at the hydrostatic bearings 21 and 22, and the rigid beams 27 and 28 are installed to hydrostatic bearing position setting apparatuses 31 and 32 fixed to the housings 15 and 17. The hydrostatic bearing position setting apparatuses 31 and 32 are provided with hydrostatic pressing force detecting apparatuses 41 and 42 such that a press support force of the hydrostatic bearings 21 and 22 can be detected.

[0060] Although a screw type is shown for the hydrostatic bearing position setting apparatuses 31 and 32 in FIG. 2, a cylinder type may be adopted. Further, the hydrostatic press force detecting apparatuses 41 and 42 may be means for directly detecting pressure other than load cells.

[0061] Next, an explanation will be given of effectiveness of supporting the work roll 3 by both of the both ends support rolls 9, 10, 11 and 12 and the hydrostatic bearings 21 and 23.

[0062] Force S in the horizontal direction exerted to the work roll 3 is as illustrated in FIG. 3 and represented by the following equation.

S=Ft+(Tb−Tf)/2

[0063] where notation Ft designates a drive tangential force based on torque T of the intermediate roll 5 supporting the work roll 3 in the up and down direction, notation Tb designates an entry side tension exerted to the strip 1 and notation Tf designates a delivery side tension exerted to the strip 1. Normally, the front and rear tensions Tb and Tf are set substantially to the same value and accordingly, the above equation normally becomes S=Ft.

[0064]FIG. 4A shows a model of a mode when horizontal bending caused in the work roll 3 by rolling is supported by using the first embodiment as an example and FIG. 4B illustrates a bending amount δ caused in the work roll 3 at the occasion. A distance between both end support portions is designated by notation L, a length Lb of the hydrostatic bearing is set to 0.83 L, and FIG. 5 shows the axial bending δ in three cases of the sheet width W of 0.83 L (in correspondence with a₀, a), 0.67 L (in correspondence with b) and 0.5 L (in correspondence with c, c′). FIG. 6 shows a calculation result of reaction Rc (in correspondence with load side) of the both end portion supporting points at that occasion in a ratio thereof to a value (a₀) in the case of both end simple support.

[0065] In FIGS. 5 and 6, since the constitution of the both end simple support corresponds to a case of pressing and supporting only areas outside of a strip path of the work roll by both ends support rolls disclosed in Japanese Patent Laid-Open No. Hei 9-285804, it is apparent that the bending is large and load at the support portion is also large as predicted.

[0066] In the meantime, when the work roll 3 is supported only by the hydrostatic bearings 21 and 23, it has already become apparent in the prior art that the attitude of the work roll 3 becomes unstable in a rolling transient condition such as when starting a rolling operation or when finishing a rolling operation and a stable support state cannot be ensured.

[0067] Curves (a), (b) and (c) shown in FIGS. 5 and 6 correspond to a state in which the both end portions of the work roll 3 are supported by the both ends support rolls 9, 10, 11 and 12 and the center portions thereof are supported by the hydrostatic bearings 21 and 23. It is apparent that in any of them, the bending δ is restrained to be small and the reaction of the both end support portions is as small as a negligible extent.

[0068] Further, in the case (c) where the sheet width W is narrow, there is provided a result showing that a direction of loading the reaction is applied is reversed. This signifies that it is necessary to ensure the support by exerting a press force having a certain value or more to the both end support portions and sandwiching the work roll 3 in both sides.

[0069] Further, referring to FIG. 6, it is apparent that the load applied to the both end portions by the work roll 3 is comparatively small and accordingly, it is no problem in terms of strength to exert the press force to the both end support portions.

[0070] In this case, the support force exerted to the both end support portions by the both ends support rolls 10 and 12 on the reference side should be set so that the support force is equal to or larger than the minimum force by which slippage is not caused between the work roll 3 and the both ends support rolls 10 and 12 and is equal to or smaller than the strength allowance load of the both ends support rolls 10 and 12 on the reference side. Further, the press force exerted to the both end support portions by the both ends support rolls 9 and 11 on the pressing side may be set to a value as large as possible within the strength allowance load of the both ends support rolls 9 and 11 on the pressing side.

[0071] The above-described setting and control are carried out based on the support force and the press force detected by using the both ends support roll support force detecting apparatuses 19 and 20 on the reference side and the both ends support roll press force detecting apparatuses 39 and 40 on the pressing side.

[0072] Further, the actual setting and control is driven by, on the reference side, adjusting fluid pressure supplied to the both ends support roll position setting apparatuses 13 and 14, the hydrostatic bearing position setting apparatuses 33 and 34, and the hydrostatic bearing 23 and is driven by, on the pressing side, adjusting fluid pressure supplied to the both ends support roll pressing apparatuses 37 and 38, the hydrostatic bearing position setting apparatuses 31 and 32, and the hydrostatic bearing 21.

[0073] Further, as shown by FIG. 7, by installing two or more of both ends support rolls 9 and 9′ or 11 and 11′ respectively on one side of the respective end portions of the work roll 3, supporting and pressing of the work roll 3 can further be ensured and accordingly, the axial bending can further be restrained.

[0074] Further, with regard to support by the hydrostatic bearings 21 and 23 at the center portion of the work roll 3, when the load is intended to be supported also on a side opposed to a side that receives the load, such force is added to the side that receives the load and accordingly, the axial bending is increased and the burden is also enlarged. Therefore, it is necessary that the burden is not applied to the bearing on the side that receives the load by using the hydrostatic bearings 21 and 23 only at the side that receives the load and not using the hydrostatic bearing on the opposed side or supporting thereof by a small force. This is made possible by adopting the constitution in which the respective end portions of the work roll 3 are pressed, sandwiched and firmly supported by the both ends support rolls 10 and 12 on the reference side and the both ends support rolls 9 and 11 on the pressing side opposed to each other.

[0075] Further, the side that receives the load can be changed to both entry side and delivery side directions of the rolling pass direction depending on an offset amount of the work roll 3, mentioned later, or other rolling conditions and therefore, it is necessary to determine the hydrostatic bearing to be used based on the rolling mill setting conditions at that occasion.

[0076] Further, as is apparent from FIG. 5, in the case (c) where the sheet width is narrow, the bending curve of the work roll 3 becomes W type. This is because the drive tangential force Ft received by the work roll 3 from the intermediate roll 5 is effectively received only by the sheet width area and at areas on outer sides of the sheet width, and the support force from the hydrostatic bearing 23 on the opposed side effects significant influence. There is a possibility of effecting an adverse influence in terms of rolling operation to the shape of the strip 2.

[0077] In contrast thereto, (c′) shows a case in which the calculation is carried out on condition that the length Lb of the hydrostatic bearing is the same as that of the sheet width W and in that case, the bending curve become smooth and the direction of the reaction at the both end support portions is stabilized without being reversed. Therefore, it is preferable in the hydrostatic bearings 21 and 23 to set an effective support length as long as the sheet width by changing the length in accordance with the sheet width W of the strip 2.

[0078] As a specific constitution to realize the above-mention setting, there is provided a method in which, for example, as shown by FIG. 8, a fluid pressure circuit 44 for supplying a fluid to a plurality of pockets 43 of the hydrostatic bearing 21 is constituted by separate paths in the width direction, the pockets 43 are selected by means of valves or the like in accordance with the sheet width W and supply of hydraulic pressure is distributed.

[0079] Further, the present invention is similarly applicable also to a case in which there is a positional shift (offset) in the rolling pass direction between the work roll 3 and the intermediate roll 5 supporting the work roll 3 in the up and down direction. That is, when there is not the offset amount, the force S in the horizontal direction exerted to the work roll 3 is as follows.

S=Ft+(Tb−Tf)/2

[0080] In contrast thereto, when the offset amount y is set as shown by FIG. 9, by taking a horizontal direction component Fp of the rolling load P into consideration as shown in the following equation, the case can be dealt with similarly to the case in which the offset is not provided.

S=Ft−Fp+(Tb−Tf)/2

[0081] Next, FIG. 10 is a vertical sectional view of principal portions of strip rolling mill 46 according to a second embodiment of the present invention and FIG. 11 is a horizontal sectional view of principal portions of the strip rolling mill 46.

[0082] In these drawings, a point of difference from the first embodiment resides in that according to the first embodiment, the barrel center portions of the work rolls 3 and 4 are supported in the horizontal direction directly by the hydrostatic bearings 21, 22, 23 and 24, whereas according to the second embodiment, undriven idle rolls 47, 48, 49 and 50 are arranged between the work rolls 3 and 4 and the hydrostatic bearings 21, 22, 23 and 24 and the work rolls 3 and 4 are supported via the idle rolls 47, 48, 49 and 50. In the rolling operation, the work rolls 3 and 4 are sometimes ground and reused, and at that occasion, diameters of the work rolls 3 and 4 are changed. On the contrary, since the hydrostatic bearings 21, 22, 23 and 24 are continuously used, inner diameters and dimensions of the bearings are not changed. As a result, the gaps between the work rolls 3 and 4 and the bearings are changed, and it is difficult to ensure the proper float up amount and the support force. Therefore, the second embodiment is preferable in view of a drawback in practice.

[0083]FIG. 12 is a vertical sectional view of principal portions of a strip rolling mill 51 according to a third embodiment of the present invention and FIG. 13 is a horizontal sectional view of principal portions of the strip roll mill 51.

[0084] In these drawings, a point of difference from the second embodiment resides in that the second embodiment is constructed by the constitution in which the both ends support roll position setting apparatuses 13 and 14 on the reference side and the both ends support roll pressing apparatuses 37 and 38 on the pressing side are respectively installed and fixed to the housings 15, 16, 17 and 18, whereas according to the third embodiment, the both ends support roll position setting apparatuses 13 and 14 on the reference side are installed to the reference side rigid beam 29 and the both ends support roll position pressing apparatuses 37 and 38 on the pressing side are installed on the pressing side rigid beam 27 to thereby integrally constitute respectively total support apparatuses 52 and 54.

[0085] It is necessary to set between the both ends support rolls 9, 10, 11 and 12 and the hydrostatic bearings 27 and 29 (or idle rolls 47 and 49) to a pertinent relative positional relationship in terms of respective functions thereof and when the both ends support rolls 9, 10, 11 and 12 and the hydrostatic bearings 21 and 23 are separately installed as in the above-described other embodiments, the relative positional relationship is to be accurately set in accordance with a reference provided for a certain separate member, resulting in troublesome operations.

[0086] In contrast thereto, by adopting the constitution as in the third embodiment, there is exhibited an advantage that by only setting the positional relationship of the respective both ends support rolls 9, 10, 11 and 12 with respect to the total support apparatuses 52 and 54, the relative positional relationship between the rolls and the hydrostatic bearings 27 and 29 can simply be set.

[0087] However, when calculating the load, the hydrostatic support force detecting apparatuses 35 and 36 detect a summed-up force of a total (total support force) including the both end support force and accordingly, when only the hydrostatic support force exerted to the hydrostatic bearing 23 is detected, it is necessary to calculate the hydrostatic support force by subtracting the both ends support force from the total support force.

[0088] According to the invention, the horizontal direction bending of the work roll caused in the rolling transient condition such as when starting the rolling operation or when finishing the rolling operation can effectively be shared by means of the both ends support rolls and the hydrostatic bearings to thereby surely support the work roll.

[0089] Further, according to the present invention, even if the work roll is ground and the diameter thereof is changed, the work roll can always be supported pertinently by the hydrostatic bearings via contact of the idle rolls.

[0090] Further, according to the present invention, by only setting the positional relationship of the respective both ends support rolls with respect to the respective total support apparatuses, the relative positional relationship between the hydrostatic bearings and the rolls can accurately be set and pertinent support can be carried out. 

What is claimed is:
 1. A strip rolling mill comprising: at least a pair of upper and lower work rolls for rolling strip; at least a pair of backup rolls for supporting the work rolls in an up and down direction and providing a rolling drive force thereto; at least pairs of both ends support rolls opposed to each other in a horizontal direction for pressing and sandwiching both end portions of the work rolls on outer sides of a width along which a maximum sheet width of the strip passes on barrel portions of the work rolls; and hydrostatic bearings for supporting, by hydraulic pressure, at least either one of an entry side and a delivery side of centers of the barrel portions of the work rolls substantially in a horizontal direction.
 2. A strip rolling mill comprising: at least a pair of upper and lower work rolls for rolling strip; at least a pair of backup rolls for supporting the work rolls in an up and down direction and providing a rolling drive force thereto; at least pairs of both ends support rolls opposed to each other in a horizontal direction for pressing and sandwiching both end portions of the work rolls on outer sides of a width along which a maximum sheet width of the strip passes on barrel portions of the work rolls; and hydrostatic bearings for supporting, by hydraulic pressure via at least one or more of idle rolls, at least either one of an entry side and a delivery side of centers of the barrel portions of the work rolls substantially in a horizontal direction.
 3. The strip rolling mill according to claim 1 or claim 2 : wherein a total support apparatus integrally formed by support portions for the both ends support rolls and support portions for the hydrostatic bearings are installed to be capable of adjusting the position of the work rolls in the horizontal direction at either one of the entry side and the delivery side of the work rolls as a reference side; and wherein on opposed sides of the work rolls, as pressing side, the total support apparatus are installed to be capable of pressing the work rolls in the horizontal direction opposedly to the reference side.
 4. The strip rolling mill according to claim 1 or claim 2 : wherein when supporting the work roll by the hydrostatic bearing, the work roll is supported on a side of receiving a load by rolling and on an opposed side, the work roll is supported in noncontact or slight contact with the hydrostatic bearing.
 5. The strip rolling mill according to any one of claims 1 through 4, further comprising: load detecting means provided at support portions for at least one of the both ends support rolls on at least one of the entry side and the delivery side and for at least one of the hydrostatic bearings.
 6. The strip rolling mill according to any one of claims 1 through 5: wherein the support force in the horizontal direction of the both ends support roll supporting portions on the reference side is controlled to be larger than a slip occurrence limit value between the work rolls and the both ends support rolls but to be smaller than a support limit value of the both ends support rolls; and wherein the press force of the both ends support rolls on the pressing side is controlled to be larger than the slip occurrence limit value between the work rolls and the both ends support rolls and to be as large as possible within a range equal to or smaller than the support limit value of the both ends support rolls.
 7. The strip rolling mill according to any one of claims 1 through 6, further comprising: means for variably controlling an effective length of the hydrostatic bearing to be substantially the same as a sheet width of the strip.
 8. A strip rolling method of rolling strip by supporting the work rolls in the horizontal direction by means of the both ends support rolls and the hydrostatic bearings using the strip rolling mill according to claim 1 or 2 .
 9. A strip rolling method of rolling strip by a pair of upper and lower work rolls, comprising the steps of: pressing and sandwiching, by at least pairs of both ends support rolls opposed to each other in a horizontal direction, both end portions of the work rolls on outer sides of a width along which a maximum sheet width of the strip passes on barrel portions of the work rolls; and supporting, by hydraulic pressure of hydrostatic bearings, at least either one of an entry side and a delivery side of centers of the barrel portions of the work rolls substantially in a horizontal direction.
 10. A strip rolling method of rolling strip, comprising the steps of: rolling strip by a pair of upper and lower work rolls; supporting the work rolls in an up and down direction and providing a rolling drive force at least by a pair of backup rolls; pressing and sandwiching, by at least pairs of both ends support rolls opposed to each other in a horizontal direction, both end portions of the work rolls on outer sides of a width along which a maximum sheet width of the strip passes on barrel portions of the work rolls; and supporting, by hydraulic pressure of hydrostatic bearings, at least either one of an entry side and a delivery side of centers of the barrel portions of the work rolls substantially in a horizontal direction. 